The interconnection of a number of electrical equipment for supervisory control and data acquisition is described within U.S. patent application Ser. No. 08/628,533 filed Apr. 3, 1996 entitled "Dynamic Data Exchange Server Simulator". The electrical equipment is interconnected within a LAN utilizing a Modbus protocol which is a trademark of New Modicon Inc. for RS-485 data format.
When a personal computer is to be connected with the LAN to interrogate the status of any of the equipment, the computer modem port is temporarily connected with the LAN by means of the modem port that is adapted for receiving data in RS-232 data format. Additional software must be included within the personal computer and the connector cable must be adapted for direct connection with the LAN.
One example of a method for interrogating a circuit breaker operating within a LAN is found in U.S. Pat. No. 5,596,473 entitled "Electrical Switches With Current Protection Interfaced With A Remote Station and A Portable Local Unit".
Various modules are commercially available for connecting between RS-232 data format and proprietary protocol used within most LAN systems as described within the following U.S. patents.
U.S. Pat. No. 5,127,090 entitled "Map Interface Unit (MAP) for Industrial Programmable Logic Controllers" describes a manufacturing automation protocol (MAP) interface unit that couples a LAN, connecting with programmable logic controllers, to a MAP network.
U.S. Pat. No. 5,245,703 entitled "Data Processing System With Multiple Communication Buses and Protocols" discloses an interface unit for connecting between internal and external communication buses having different protocols.
U.S. Pat. No. 5,355,365 entitled "Intelligent Local Area Network Modem Mode" describes a LAN modem node that allows PC's on the LAN to communicate with off-LAN PC's, printers and other local area networks.
When there is a need for a host PC to communicate with any of the electrical equipment on the LAN, as described within the aforementioned U.S. patent application Ser. No. 08/628,533, it would be convenient to interpose a monitor unit having capacity to receive both RS-232 configured and RS-485 configured plug sockets along with the capacity to translate between the associated RS-232 and RS-485 protocols.
One purpose of the invention, accordingly, is to provide a stand-alone monitor unit that allows external connection with a dedicated LAN by use of standard PC connector cables.